Peripheral T-cell Lymphoma (PTCL) encompasses a heterogonous group of clinically aggressive entities. Using current diagnostic approaches, more than a third cannot be classified and are designated as PTCL-not otherwise specified (PTCL-NOS). Using gene expression profiling (GEP), we delineated two novel major molecular subgroups in PTCL-NOS with distinct clinical and biological features. The first (PTCL-GATA3) is characterized by high expression of GATA3, a master regulator of T helper2 (TH2) differentiation and its target genes, whereas the second (PTCL-TBX21) is characterized by high expression of TBX21, master regulator of TH1 differentiation and its target genes, with the former showing significantly worse outcome. Preliminary genetic characterizations showed distinct patterns of chromosomal copy number abnormalities (CNAs) associated with significant enrichment of distinct oncogenic pathways. The long-term goal of the research is to define the mechanisms that determine the biology of these subgroups with the intention of identifying new targets and strategies for effective treatment, with special emphasis on the PTCL-GATA3 subgroup. This goal will be accomplished through three Specific Aims: (1) to determine the mutational landscape of the PTCL- GATA3 and PTCL-TBX21 subgroups. We hypothesize that deciphering the genetic mutational landscape of PTCL-GATA3 and PTCL-TBX21 will delineate the mechanistic basis of the differences in biology and clinical- outcome. We will perform whole exome- and RNA-sequencing (WES and RNA-seq) analysis on a well-defined cohort of PTCLs. A targeted capture panel will be established based on WES data to further determine the mutational incidence using formalin-fixed paraffin-embedded tissue (FFPET) in a large PTCL cohort including relapsed/refractory PTCL; (2) to delineate the role of combined PTEN and p53 loss in the pathobiology of the PTCL-GATA3 subgroup. We previously identified frequent co-occurrence of deletions of genomic loci encompassing pten and p53 in the PTCL-GATA3 subgroup but not in the PTCL-TBX21 subgroup. These genetic lesions may have functional consequences other than their canonical role in regulating the phosphatidylinositol 3-kinase (PI3K) pathway and genomic integrity. We hypothesize that pten and p53 loss cooperates in the oncogenic transformation of T-cells partly through deregulation of T cell differentiation. We will use both murine models and genetically modified human T-cells for this study; (3) to evaluate treatments targeting activated oncogenic pathways in the PTCL-GATA3 subgroup. No representative cell lines or animal models of poorest prognosis, PTCL-GATA3, subgroup are currently available. We hypothesize that well characterized PTCL PDTX models can serve as pre-clinical models for evaluating the efficacy of novel drugs in cases with dual pten/p53 loss. This Project will use Pathology Core 1, Biostatistics/Bioinformatics Core 4, Pre-Clinical Models and Therapeutics Core 3, and Functional Genomics Core 2 to accomplish these Aims.